This invention relates to forming of diffusion bonded joints in superplastically formed hollow metal structures and in particular to the joint integrity of peripheral diffusion bonded joints between adjacent sheets of material following removal of an external flange from the region of the joint.
The term `superplastic forming` used in this specification refers to characteristics exhibited by a known class of metallic alloys which have a composition and microstructure such that when heated to within an appropriate temperature range and deformed within an appropriate range of strain rate, the metal takes on the flow characteristics of a plastic material, that is to say it has the flow characteristics of a viscous fluid. With such metallic alloys, large deformations are possible without fracture. The term `diffusion bonding` used in this specification refers to a process which forms a metallurgical bond by the application of heat and pressure to metal pieces held in close contact for a given length of time.